(1) Field of the Invention
U.S. CLASS 418, Rotary Expansible Chamber Devices                U.S. CLASS 418/225        
(2) Description of Related Art
Rotary pumps and rotary motors have some major limitations, e.g. radial friction between the moving parts and housing wall would cause significant frictional loss and unacceptable wear so the device was inefficient and won't last long.
Furthermore, a rotary machine to replace the conventional piston-crankshaft engine was a long time effort since James Watt's three-vane rotary of 1782, including Felix Wankel in the 1950s and US patent 2008/0310985 A1 by Sorby Reider dated December 2008; but unfortunately none of them succeeded as expected.
By analyzing all the prior designs, the problems were largely caused by the dynamic sealing for a variable enclosed space, and friction between the housing and moving parts.
So nevertheless how attractive could be the promises and advantages, unless these difficulties are overcome, the rotary engine was always a delusion to all inventors, for a couple of hundred years in the past.